1. Field of the Disclosure
Embodiments disclosed herein relate generally to systems and methods for producing slurries for re-injection at a work site. More specifically, embodiments disclosed herein relate to systems and methods for slurrifying drill cuttings for re-injection at a work site.
2. Background
In the drilling of wells, a drill bit is used to dig many thousands of feet into the earth's crust. Oil rigs typically employ a derrick that extends above the well drilling platform. The derrick supports joint after joint of drill pipe connected end-to-end during the drilling operation. As the drill bit is pushed further into the earth, additional pipe joints are added to the ever lengthening “string” or “drill string”. Therefore, the drill string includes a plurality of joints of pipe.
Fluid “drilling mud” is pumped from the well drilling platform, through the drill string, and to a drill bit supported at the lower or distal end of the drill string. The drilling mud lubricates the drill bit and carries away well cuttings generated by the drill bit as it digs deeper. The cuttings are carried in a return flow stream of drilling mud through the well annulus and back to the well drilling platform at the earth's surface. When the drilling mud reaches the platform, it is contaminated with small pieces of shale and rock that are known in the industry as well cuttings or drill cuttings. Once the drill cuttings, drilling mud, and other waste reach the platform, a “shale shaker” is typically used to remove the drilling mud from the drill cuttings so that the drilling mud may be reused. The remaining drill cuttings, waste, and residual drilling mud are then transferred to a holding trough for disposal. In some situations, for example with specific types of drilling mud, the drilling mud may not be reused and it must be disposed. Typically, the non-recycled drilling mud is disposed of separate from the drill cuttings and other waste by transporting the drilling mud via a vessel to a disposal site.
The disposal of the drill cuttings and drilling mud is a complex environmental problem. Drill cuttings contain not only the residual drilling mud product that would contaminate the surrounding environment, but may also contain oil and other waste that is particularly hazardous to the environment, especially when drilling in a marine environment.
In the Gulf of Mexico, for example, there are hundreds of drilling platforms that drill for oil and gas by drilling into the subsea floor. These drilling platforms may be used in places where the depth of the water is many hundreds of feet. In such a marine environment, the water is typically filled with marine life that cannot tolerate the disposal of drill cuttings waste. Therefore, there is a need for a simple, yet workable solution to the problem of disposing of well cuttings, drilling mud, and/or other waste in marine and other fragile environments.
Traditional methods of disposal include dumping, bucket transport, cumbersome conveyor belts, screw conveyors, and washing techniques that require large amounts of water. Adding water creates additional problems of added volume and bulk, pollution, and transport problems. Installing conveyors requires major modification to the rig area and involves extensive installation hours and expense.
Another method of disposal includes returning the drill cuttings, drilling mud, and/or other waste via injection under high pressure into an earth formation. Generally, the injection process involves the preparation of a slurry within surface-based equipment and pumping the slurry into a well that extends relatively deep underground into a receiving stratum or adequate formation. The basic steps in the process include the identification of an appropriate stratum or formation for the injection; preparing an appropriate injection well; formulation of the slurry, which includes considering such factors as weight, solids content, pH, gels, etc.; performing the injection operations, which includes determining and monitoring pump rates such as volume per unit time and pressure; and capping the well.
In some instances, the cuttings, which are still contaminated with some oil, are transported from a drilling rig to an offshore rig or ashore in the form of a thick heavy paste or slurry for injection into an earth formation. Typically the material is put into special skips of about 10 ton capacity that are loaded by crane from the rig onto supply boats. This is a difficult and dangerous operation that may be laborious and expensive.
U.S. Pat. No. 6,709,216 and related patent family members disclose that cuttings may also be conveyed to and stored in an enclosed, transportable vessel, where the vessel may then be transported to a destination, and the drill cuttings may be withdrawn. The transportable storage vessel has a lower conical section structured to achieve mass flow of the mixture in the vessel, and withdrawal of the cuttings includes applying a compressed gas to the cuttings in the vessel. The transportable vessels are designed to fit within a 20 foot ISO container frame. These conical vessels will be referred to herein as ISO vessels.
As described in U.S. Pat. No. 6,709,216 and family, the ISO vessels may be lifted onto a drilling rig by a rig crane and used to store cuttings. The vessels may then be used to transfer the cuttings onto a supply boat, and may also serve as buffer storage while a supply boat is not present. Alternatively, the storage vessels may be lifted off the rig by cranes and transported by a supply boat.
Space on offshore platforms is limited. In addition to the storage and transfer of cuttings, many additional operations take place on a drilling rig, including tank cleaning, slurriflcation operations, drilling, chemical treatment operations, raw material storage, mud preparation, mud recycle, mud separations, and others.
Due to the limited space, these operations may be modularized, in which modules are swapped out when not needed or when space is needed for the equipment. For example, cuttings containers may be offloaded from the rig to make room for modularized equipment used for slurrification. These lifting operations, as mentioned above, are difficult, dangerous, and expensive. Additionally, many of these modularized operations include redundant equipment, such as pumps, valves, and tanks or storage vessels.
Slurrifications systems that may be moved onto a rig are typically large modules that are fully self-contained, receiving cuttings from a drilling rig's fluid mud recovery system. For example, PCT Publication No. WO 99/04134 discloses a process module containing a first slurry tank, grinding pumps, a system shale shaker, a second slurry tank, and optionally a holding tank. The module may be lifted by a crane on to an offshore drilling platform.
Slurrification systems may also be disposed in portable units that may be transported from one work site to another. As disclosed in U.S. Pat. No. 5,303,786, a slurriflcation system may be mounted on a semi-trailer that may be towed between work sites. The system includes, inter alia, multiple tanks, pumps, mills, grinders, agitators, hoppers, and conveyors. As discussed in U.S. Pat. No. 5,303,786, the slurrification system may be moved to a site where a large quantity of material to be treated is available, such as existing or abandoned reserve pits that hold large quantities of cuttings.
U.S. Pat. No. 6,745,856 discloses another transportable slurrification system that is disposed on a transport vehicle. The transport vehicle (i.e., a vessel or boat) is stationed proximate the work site (i.e., offshore platform) and connected to equipment located at the work site while in operation. Deleterious material is transferred from the work site to the transport vehicle, wherein the deleterious material is slurrified. The slurry may be transferred back to the work site for, in one example, re-injection into the formation. Alternatively, the slurry may be transported via the transport vehicle to a disposal site. As disclosed in U.S. Pat. No. 6,745,856, storage vessels are disposed on the transport vehicle for containing the slurry during transportation. While in-transit to the disposal site, agitators disposed in the storage vessels may agitate the slurry to keep the solids suspended in the fluid.
While these systems and methods provide improved processes in slurrification and re-injection systems, they require difficult, dangerous, and expensive lifting and installation operations, as described above. Additionally, these processes may require lengthy installation and processing times that may reduce the overall efficiency of the work site.
A slurrification system is used to create a slurry for a cuttings re-injection system. Typically, slurrification systems receive cuttings and convert them into a pumpable slurry. Elements of a slurrification system generally include a fine-solids (“fines”) tank, a coarse-solids (“coarse”) tank, a classification system, and a storage vessel, wherein drill cuttings are dried, separated, and transferred to a cuttings re-injection system or stored for further processing. After preparation of the slurry, the slurry is pumped to a storage vessel, until an injection pump is used to pump the slurry down a wellbore.
In operation, attempts to produce a slurry that meet local environmental regulations and operational regulations has proven problematic. Current slurrification systems are operationally inefficient. For example, adjustments to the drilling operation including adjustments to cuttings volume production and rate of penetration of the wellbore may cause slurrification process and cuttings re-injection inefficiencies. Moreover, increasingly stringent cuttings-discharge regulations have pressured operators and drilling contractors to reduce drilling waste volumes and recover products for re-use. Thus, there exists a continuing need for more efficient slurrification methods and systems, specifically, for slurrification systems for use in preparing slurries for re-injecting cuttings into a wellbore.